As a fleet ages, performance should be assessed by matched conditions rather than calendar age. Keep temperature records, and also record the product, load, ambient profile, door openings, route and operating mode behind each record. Longer unit operation or higher fuel use may be a symptom, but neither diagnoses a fault alone.
Separate age from condition. Comparing the same vehicle with the same month last year is meaningful only when load, ambient profile, door openings, operating mode and route are comparable. A season or calendar month does not create matched conditions by itself. Keep temperature, unit-hour and product-acceptance results together; an in-band record does not make extra duty invisible. Match route and operating conditions as described in the refrigeration fuel guide.
| Stage | Baseline | Current context | Next check |
|---|---|---|---|
| Reference | Product, load, ambient, route, doors and mode | Valid reading and acceptance result | Repeat under matched conditions |
| Monitoring | Temperature record, unit hours, energy/fuel | Measurement point and period | Separate change by context |
| Symptom | Slow pull-down, repeated alarm, longer duty | Body, unit and load distinction | Request qualified technical check |
| Decision | Service, overhaul, backup or replacement candidate | Cost and operational effect | Write evidence and assumptions |
Separate body from unit
When comparing empty-body cool-down time, record initial air and wall temperatures, target, ambient conditions and operating mode. The test reflects the whole system; it does not by itself establish whether a delay comes from the body or the unit. Doors, gaskets and panel joints require separate checks from unit sensors and control cycles. Keep product-temperature and box-air measurements distinct, and identify the sensor position in each record.
Turn a symptom into a technical question
If pull-down takes longer, alarms recur or the unit runs longer than expected, request a check while preserving the recorded conditions. A driver or fleet manager observation does not replace qualified inspection. Do not infer a leak, fan, compressor or insulation fault from fuel, electricity, engine hours or a display change.
Compare alternatives using the same data
For a service or overhaul candidate, record the existing history, parts condition, control cycles and expected duty. If a passive backup validated for the route and product is considered, plan freezing energy, coolant mass, preparation space, temperature logging and return/cleaning workflow separately. A passive container is not automatically a cheap equivalent to an ageing refrigeration unit; compare it on the same route and product conditions.
Build the service record
Each check records model, serial number, unit hours, operating mode, product/load, ambient conditions, door openings, sensor positions, temperature result, finding, work completed and next-check date. Keep empty-body tests, loaded routes and service findings as separate evidence types in one file.
The April 2022 Thermo King Precedent C-600M, S-610M and S-610DE manual distinguishes Cycle-Sentry automatic start/stop from continuous airflow (pp. 23-24). Because of that distinction, mark mode changes in fleet comparisons instead of attributing more running hours directly to wear. For replacement decisions, use the component records in the service-life guide.
Do not make an ageing decision from one number. Comparable temperature records, matched operating conditions, body-versus-unit separation, service findings and the real preparation and return workload of a backup option make a service, overhaul or replacement candidate defensible.
